Secondary battery and battery pack including the same

ABSTRACT

Provided are a secondary battery and a battery pack including the secondary battery. A sealing plate has a positive electrode terminal attachment hole. A positive electrode terminal penetrates the positive electrode terminal attachment hole. An external conductive member is connected to a portion of the positive electrode terminal located on the battery outer side with respect to the sealing plate. The conduction path between a positive electrode plate and the positive electrode terminal is provided with a current interrupting mechanism. A first insulating member made of resin is disposed between the sealing plate and the positive electrode terminal. A second insulating member having higher thermal resistance than the first insulating member is disposed between the external conductive member and the sealing plate.

CROSS REFERENCE TO RELATED APPLICATIONS

The present invention application claims priority to Japanese PatentApplication No. 2018-037101 filed in the Japan Patent Office on Mar. 2,2018, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a secondary battery and a battery packincluding the secondary battery.

Description of Related Art

Non-aqueous electrolyte secondary batteries are used as driving powersources for electric vehicles (EVs) and hybrid electric vehicles (HEVs,PHEVs), and as stationary storage battery systems, for example, for usein reducing the output fluctuations of solar power, wind power, andother resources, and for use in peak shift of grid-connected power tostore power at night and use it for daytime. These applications usesecondary batteries connected in parallel.

For these secondary batteries, Japanese Published Unexamined PatentApplication Nos. 2016-119210 and 2013-089592 (Patent Documents 1 and 2)disclose techniques for disposing a current interrupting mechanism or afuse part in the conduction path between an electrode body and aterminal to improve reliability.

The current interrupting mechanism operates in response to an increasein the internal pressure of the battery case. The fuse part melts andbreaks upon the flow of a large current.

BRIEF SUMMARY OF THE INVENTION

A secondary battery and a battery pack including the secondary batteryneed to have high reliability in case of a short circuit that may occurinside the secondary battery.

An object of the present invention is to provide a secondary batteryhaving high reliability and a battery pack including the secondarybattery.

A secondary battery in an aspect of the present invention includes anelectrode body that includes a positive electrode plate and a negativeelectrode plate; an outer body that has an opening and houses theelectrode body; a sealing plate that is made of metal and seals theopening; and a terminal that is electrically connected to the positiveelectrode plate or the negative electrode plate. The sealing plate has aterminal attachment hole. The terminal penetrates the terminalattachment hole. An external conductive member is connected to a portionof the terminal located on a battery outer side with respect to thesealing plate. A conduction path between the positive electrode plate orthe negative electrode plate and the terminal is provided with at leastone of a current interrupting mechanism and a fuse part. A firstinsulating member made of resin is disposed between the sealing plateand the terminal.

A second insulating member having higher thermal resistance than thefirst insulating member is disposed between the external conductivemember and the sealing plate.

The inventors of the present invention have found that there is thefollowing issue in a battery pack including secondary batteries that areconnected in parallel and each have at least one of a currentinterrupting mechanism and a fuse part in a conduction path between theelectrode body and the terminal.

In the case where secondary batteries are connected in parallel and ashort circuit occurs between positive and negative electrodes in onesecondary battery, a current flows into the secondary battery in whichthe short circuit has occurred from other secondary batteries connectedin parallel. Thus, the secondary battery in which the short circuit hasoccurred in the case where secondary batteries are connected in paralleltends to become a higher-temperature state than that in the case wheresecondary batteries are not connected in parallel. When the secondarybattery becomes a high-temperature state, the electrolyte decomposes toincrease the pressure of gas in the battery case, and the currentinterrupting mechanism operates. Since the operation of the currentinterrupting mechanism causes disconnection of the conduction pathbetween the electrode body and the terminal, the current flow from othersecondary batteries into the secondary battery in which the shortcircuit has occurred is terminated.

In the case where secondary batteries each have a fuse part and a shortcircuit occurs between positive and negative electrodes in one secondarybattery, the fuse part melts and breaks due to a short-circuit currentto disconnect the conduction path between the electrode body and theterminal. Thus, the current flow from other secondary batteries into thesecondary battery in which the short circuit has occurred is terminated.

However, even when the current flow from other secondary batteries intothe secondary battery in which the short circuit has occurred isterminated, the chemical reaction inside the battery or the like maymaintain the high-temperature state of the secondary battery in whichthe short circuit has occurred or may increase the temperature of thesecondary battery in which the short circuit has occurred. In the casewhere the secondary battery becomes a high-temperature state, there is apossibility that an insulating member made of resin that insulatesbetween the terminal and the sealing plate may melt. If an insulatingmember made of resin between a positive electrode terminal and thesealing plate and an insulating member made of resin between a negativeelectrode terminal and the sealing plate both melt, the positiveelectrode terminal and the negative electrode terminal are eachelectrically connected to the sealing plate. This forms a conductionpath of positive electrode terminal-sealing plate-negative electrodeterminal and thus forms a closed circuit between the secondary batteriesconnected in parallel. Then, a current flows in the secondary batteriesconnected in parallel, and a large current flows in the secondarybatteries connected in parallel to the secondary battery in which theshort circuit has occurred. As a result, an abnormal event may occur inthe secondary batteries connected in parallel to the secondary batteryin which the short circuit has occurred.

In the structure of the secondary battery in one aspect described above,the thermal resistance of the second insulating member connected to theterminal and disposed between the external conductive member and thesealing plate is higher than the thermal resistance of the firstinsulating member made of resin and disposed between the terminal andthe sealing plate. Therefore, even if the secondary battery becomes ahigh-temperature state so that the first insulating member melts, thesecond insulating member can suppress a reduction in the distancebetween the sealing plate and the external conductive member connectedto the terminal. The second insulating member can thus avoid the contactbetween the terminal and the sealing plate caused by movement of theterminal, which is connected to the external conductive member, towardthe sealing plate. Therefore, even if a short circuit occurs inside oneof the secondary batteries connected in parallel, occurrence of abnormalevents in secondary batteries different from the secondary battery inwhich the short circuit has occurred can be effectively suppressed.

Here, the expression the thermal resistance of the second insulatingmember is higher than the thermal resistance of the first insulatingmember means that the highest temperature at which the second insulatingmember can keep the distance between the external conductive member andthe sealing plate is higher than the highest temperature at which thefirst insulating member can keep the distance between the terminal andthe sealing plate.

For example, the second insulating member may be composed of a materialhaving a higher melting point than the material that constitutes thefirst insulating member.

The external conductive member can be a member to which a busbar thatelectrically connects secondary batteries to each other in the batterypack is connected. In this case, a bolt is connected to the conductivemember so that the busbar can be fixed to the external conductive memberthrough the bolt. The busbar may be weld-connected to the externalconductive member. In this case, the bolt is not necessary.

The busbar that electrically connects secondary batteries to each othermay serve an external conductive member.

The present invention can provide a secondary battery with highreliability and a battery pack including the secondary battery.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A is a top view of a prismatic secondary battery according to anembodiment, and FIG. 1B is a side view of the prismatic secondarybattery according to the embodiment;

FIG. 2A is a cross-sectional view taken along line IIA-IIA in FIG. 1A,FIG. 2B is a cross-sectional view taken along line IIB-IIB in FIG. 2A,and FIG. 2C is a cross-sectional view taken along line IIC-IIC in FIG.2A;

FIG. 3 is a cross-sectional view of a current interrupting mechanism andthe surrounding area in the transverse direction of the sealing plate;

FIG. 4 is a cross-sectional view of the current interrupting mechanismand the surrounding area in the longitudinal direction of the sealingplate;

FIG. 5 is a top view of a battery pack including a plurality of theprismatic secondary batteries according to the embodiment;

FIG. 6 is a view corresponding to FIG. 4 for a prismatic secondarybattery according to Modification 1;

FIG. 7 is a view corresponding to FIG. 4 for a prismatic secondarybattery according to Modification 2;

FIG. 8 is a view corresponding to FIG. 4 for a prismatic secondarybattery according to Modification 3;

FIG. 9 is a view corresponding to FIG. 4 for a prismatic secondarybattery according to Modification 4; and

FIG. 10 is a view corresponding to FIG. 4 for a prismatic secondarybattery according to Modification 5.

DETAILED DESCRIPTION OF THE INVENTION

The structure of a prismatic secondary battery 20, which is a secondarybattery according to an embodiment, will be described below. The presentinvention is not limited to the following embodiment.

As illustrated in FIG. 1A, FIG. 1B, and FIGS. 2A to 2C, the prismaticsecondary battery 20 has a battery case 100. The battery case 100includes a bottomed cylindrical prismatic outer body 1 having anopening, and a sealing plate 2 that seals the opening of the prismaticouter body 1. The prismatic outer body 1 and the sealing plate 2 arepreferably each made of metal, and preferably made of, for example,aluminum or an aluminum alloy. The prismatic outer body 1 contains,together with an electrolyte, a flat electrode body 3 including apositive electrode plate and a negative electrode plate that are woundwith a separator interposed therebetween.

The electrode body 3 has a wound positive electrode core-exposed portion4 at one end and a wound negative electrode core-exposed portion 5 atthe other end. A positive electrode current collector 6 is connected tothe positive electrode core-exposed portion 4. The positive electrodecurrent collector 6 is electrically connected to a positive electrodeterminal 7 attached to the sealing plate 2. A negative electrode currentcollector 8 is connected to the negative electrode core-exposed portion5. The negative electrode current collector 8 is electrically connectedto a negative electrode terminal 9 attached to the sealing plate 2. Thepositive electrode current collector 6, the positive electrode terminal7, the negative electrode current collector 8, and the negativeelectrode terminal 9 are each made of metal.

A first insulating member 10 made of resin is disposed between thepositive electrode terminal 7 and the sealing plate 2. A firstinsulating member 11 made of resin is disposed between the negativeelectrode terminal 9 and the sealing plate 2. An internal insulatingmember 12 made of resin is disposed between the sealing plate 2 and thenegative electrode current collector 8.

The sealing plate 2 has an electrolyte injection port 13. Theelectrolyte injection port 13 is sealed with a sealing member 14. Thesealing plate 2 has a gas release valve 15. The gas release valve 15fractures upon an increase in the internal pressure of the battery case100 to a predetermined value or higher and releases gas from the batterycase 100 to the outside of the battery case 100.

An insulating sheet 16 made of resin is disposed between the prismaticouter body 1 and the electrode body 3. The insulating sheet 16 is formedin a bag shape or a box shape and contains the electrode body 3 inside.

The conduction path between the positive electrode plate and thepositive electrode terminal 7 is provided with a current interruptingmechanism 30. The current interrupting mechanism 30 operates when anabnormal event occurs in the prismatic secondary battery 20 to increasethe internal pressure of the battery case 100 to a predetermined valueor higher. The operation of the current interrupting mechanism 30 causesdisconnection of the conduction path between the positive electrodeplate and the positive electrode terminal 7. The operating pressure ofthe current interrupting mechanism 30 is lower than the operatingpressure of the gas release valve 15. The current interrupting mechanism30 may be provided in the conduction path between the negative electrodeplate and the negative electrode terminal 9.

The wound positive electrode core-exposed portion 4 is divided into twosections from the central part, and intermediate conductive members 50made of metal are disposed between these two sections. Two intermediateconductive members 50 are held by holding members 51 made of resin.Welds 60 are formed at the connection parts between the positiveelectrode current collector 6, the positive electrode core-exposedportion 4, and the intermediate conductive members 50.

The wound negative electrode core-exposed portion 5 is divided into twosections from the central part, and the intermediate conductive members52 made of metal are disposed between these two sections. Twointermediate conductive members 52 are held by holding members 53 madeof resin. Welds (not illustrated) are formed at the connection partsbetween the negative electrode current collector 8, the negativeelectrode core-exposed portion 5, and the intermediate conductivemembers 52.

Next, a method for producing the prismatic secondary battery 20, and thecomponents of the prismatic secondary battery 20 will be described belowin detail.

Positive Electrode Plate

A positive electrode active material mixture layer containing a positiveelectrode active material is formed on each surface of a positiveelectrode core made of metal foil to provide a strip-shaped positiveelectrode plate. The positive electrode plate has a positive electrodecore-exposed portion 4 in an edge part in the width direction. Thepositive electrode core-exposed portion 4 has no positive electrodeactive material mixture layer on each surface and extends in thelongitudinal direction of the positive electrode plate. The positiveelectrode core is preferably made of, for example, aluminum foil oraluminum alloy foil. The positive electrode active material ispreferably a lithium-transition metal composite oxide. The positiveelectrode active material mixture layer preferably contains a binder,such as polyvinylidene fluoride, and a conductive agent composed of acarbon material and other materials.

Negative Electrode Plate

A negative electrode active material mixture layer containing a negativeelectrode active material is formed on each surface of a negativeelectrode core made of metal foil to provide a strip-shaped negativeelectrode plate. The negative electrode plate has a negative electrodecore-exposed portion 5 in an edge part in the width direction. Thenegative electrode core-exposed portion 5 has no negative electrodeactive material mixture layer on each surface and extends in thelongitudinal direction of the negative electrode plate. The negativeelectrode core is preferably made of, for example, copper foil or copperalloy foil. The negative electrode active material is preferably, forexample, a carbon material or a silicon material. The negative electrodeactive material mixture layer preferably contains a binder, such ascarboxymethylcellulose (CMC) or styrene-butadiene rubber (SBR).

Electrode Body

The strip-shaped positive electrode plate and the strip-shaped negativeelectrode plate are wound with a strip-shaped separator interposedtherebetween, and formed in a flat shape to provide a flat electrodebody 3. In the electrode body 3, the wound positive electrodecore-exposed portion 4 is disposed in one edge part in the direction inwhich the winding axis extends, and the wound negative electrodecore-exposed portion 5 is disposed in the other edge part. The separatoris preferably a fine porous membrane. The separator is preferably apolyolefin separator.

Current Interrupting Mechanism

Referring to FIG. 3 and FIG. 4, a method for attaching the positiveelectrode terminal 7 to the sealing plate 2, a method for producing thecurrent interrupting mechanism 30, and the structure of the currentinterrupting mechanism 30 will be described.

The first insulating member 10 is disposed on the battery outer sidearound the positive electrode terminal attachment hole 2 a of thesealing plate 2. A third insulating member 31 and a conductive member 32are disposed on the battery inner side around the positive electrodeterminal attachment hole 2 a of the sealing plate 2. The positiveelectrode terminal 7 is inserted from the battery outer side into thethrough-hole of the first insulating member 10, the positive electrodeterminal attachment hole 2 a, the through-hole of the third insulatingmember 31, and the through-hole of the conductive member 32. The end ofthe positive electrode terminal 7 is crimped onto the conductive member32. The positive electrode terminal 7, the first insulating member 10,the third insulating member 31, and the conductive member 32 are thusfixed to the sealing plate 2. The positive electrode terminal 7 has aflange part 7 a, an insertion part 7 b, and a crimped part 7 c. Theflange part 7 a is disposed on the battery outer side with respect tothe sealing plate 2. The insertion part 7 b extends from the flange part7 a to the battery inner side. The crimped part 7 c is formed on the endside of the insertion part 7 b. The crimped part 7 c is preferablywelded to the conductive member 32. The third insulating member 31 is aresin member. The sealing plate 2 is electrically insulated from thepositive electrode terminal 7 and the conductive member 32 by the firstinsulating member 10 and the third insulating member 31.

The conductive member 32 is made of metal and has a cup shape. Theconductive member 32 has a region parallel to the sealing plate 2, and acylindrical region. The cylindrical region has an opening adjacent tothe electrode body 3. The cross-sectional shape of the cylindricalregion in the direction parallel to the sealing plate 2 may be circularor rectangular.

The positive electrode terminal 7 has a terminal through-hole 7 d. Theleak inspection of each connection part can be carried out by flowinggas from the terminal through-hole 7 d into the current interruptingmechanism 30. The terminal through-hole 7 d is sealed with a rubbermember 71. The outer surface of the rubber member 71 is preferablyprovided with a metal plate 72.

The opening of the conductive member 32 adjacent to the electrode body 3is sealed with a deformation plate 33 made of metal. A positiveelectrode current collector 6 is connected to the surface of thedeformation plate 33 adjacent to the electrode body 3. A fourthinsulating member 34 made of resin is disposed between the deformationplate 33 and the positive electrode current collector 6. The fourthinsulating member 34 is preferably connected to the third insulatingmember 31.

The positive electrode current collector 6 has a base part 6 a locatedbetween the sealing plate 2 and the electrode body 3. The base part 6 ahas a fixation opening 6 b. A fixation protrusion 34 a of the fourthinsulating member 34 is inserted into the fixation opening 6 b. Thediameter of the end of the fixation protrusion 34 a is enlarged by hotcrimping or the like, so that the fourth insulating member 34 is fixedto the base part 6 a of the positive electrode current collector 6.

The base part 6 a of the positive electrode current collector 6 has athin portion 6 c. The thin portion 6 c has a current collector opening 6d at its center. The positive electrode current collector 6 isweld-connected to the deformation plate 33 at the periphery of thecurrent collector opening 6 d.

When the internal pressure of the battery case 100 reaches apredetermined value or higher, the deformation plate 33 deforms suchthat the central part of the deformation plate 33 comes close to thepositive electrode terminal 7. The deformation of the deformation plate33 causes the thin portion 6 c of the positive electrode currentcollector 6 to fracture and thus disconnects the conduction path betweenthe positive electrode plate and the positive electrode terminal 7.Preferably, the thin portion 6 c has an annular notch and fractures atthe annular notch.

Attachment of Negative Electrode Terminal to Sealing Plate

The first insulating member 11 is disposed on the battery outer sidearound the negative electrode terminal attachment hole of the sealingplate 2. The internal insulating member 12 and the negative electrodecurrent collector 8 are disposed on the battery inner side around thenegative electrode terminal attachment hole of the sealing plate 2. Thenegative electrode terminal 9 is then inserted from the battery outerside into the through-hole of the first insulating member 11, thenegative electrode terminal attachment hole, the through-hole of theinternal insulating member 12, and the through-hole of the negativeelectrode current collector 8. The end of the negative electrodeterminal 9 is crimped onto the negative electrode current collector 8.The negative electrode terminal 9, the first insulating member 11, theinternal insulating member 12, and the negative electrode currentcollector 8 are fixed to the sealing plate 2. The crimped part of thenegative electrode terminal 9 is preferably welded to the negativeelectrode current collector 8.

Attachment of Electrode Body to Current Collector

The positive electrode current collector 6 is welded to each outersurface of the wound positive electrode core-exposed portion 4. Thenegative electrode current collector 8 is welded to each outer surfaceof the wound negative electrode core-exposed portion 5.

Assembly of Prismatic Secondary Battery

The electrode body 3 is covered with the insulating sheet 16 that hasbeen bent and formed into a box shape. The electrode body 3 is theninserted into the prismatic outer body 1. The sealing plate 2 is weldedto the prismatic outer body 1 such that the opening of the prismaticouter body 1 is closed with the sealing plate 2. An electrolyte is theninjected into the battery case 100 through the electrolyte injectionport 13 of the sealing plate 2. The electrolyte injection port 13 isthen sealed with the sealing member 14 composed of a blind rivet or thelike. The prismatic secondary battery 20 is produced in this way.

Attachment of Second Insulating Member and External Conductive Member

As illustrated in FIG. 3 and FIG. 4, an external conductive member 85 isdisposed on the sealing plate 2 with the second insulating member 80interposed therebetween. The external conductive member 85 is connectedto a portion of the positive electrode terminal 7 located on the batteryouter side with respect to the sealing plate 2. The external conductivemember 85 is made of metal. The external conductive member 85 ispreferably made of aluminum or an aluminum alloy. Preferably, theexternal conductive member 85 has a through-hole, the positive electrodeterminal 7 is disposed inside the through-hole, and the externalconductive member 85 and the positive electrode terminal 7 areweld-connected to each other. The positive electrode terminal 7 may becrimped onto the external conductive member 85. The external conductivemember 85 is disposed on a flange part 7 a of the positive electrodeterminal 7. A bolt 86 made of meal is connected to the externalconductive member 85.

The second insulating member 80 is preferably fitted to the sealingplate 2.

As illustrated in FIG. 1A and FIG. 4, the sealing plate 2 has a firstprotrusion 2 b and a second protrusion 2 c on the battery outer surface.The second insulating member 80 has an insulating member first recess 80a and an insulating member second recess 80 b. The first protrusion 2 bis located inside the insulating member first recess 80 a, and thesecond protrusion 2 c is located inside the insulating member firstrecess 80 a.

The sealing plate 2 has an annular first recess 2 d around the firstprotrusion 2 b and has an annular second recess 2 e around the secondprotrusion 2 c. Preferably, the annular insulating member firstprotrusion 80 c of the second insulating member 80 is located inside thefirst recess 2 d, and an annular insulating member second protrusion 80d of the second insulating member 80 is located inside the second recess2 e.

Alternatively, the sealing plate 2 may have a recess, and a protrusionon the second insulating member 80 may be fitted to the recess. In thiscase, the recess may be, for example, a linear recess that extends inthe longitudinal direction of the sealing plate 2. The sealing plate 2may have a plurality of the recesses. For example, the sealing plate 2may have two recesses arranged in parallel or may have four recessesarranged in parallel. The recess of the sealing plate 2 may be in adotted form, an annular form, or other form.

An external conductive member 88 is connected to a portion of thenegative electrode terminal 9 located on the battery outer side withrespect to the sealing plate 2. A second insulating member 81 isdisposed between the external conductive member 88 and the sealing plate2. The external conductive member 88 is made of metal. The externalconductive member 88 is preferably made of aluminum or an aluminumalloy. In the case where the negative electrode terminal 9 is made ofcopper or a copper alloy, a region of the external conductive member 88connected to the negative electrode terminal 9 can be made of copper ora copper alloy, and a portion of the external conductive member 88connected to the bolt 86 can be made of aluminum or an aluminum alloy.The negative electrode terminal 9 may have a portion made of copper or acopper alloy and a portion made of aluminum or an aluminum alloy. Inthis case, the external conductive member 88 made of aluminum or analuminum alloy is preferably connected to the portion of the negativeelectrode terminal 9 made of aluminum or an aluminum alloy. The negativeelectrode current collector 8 made of copper or a copper alloy ispreferably connected to the portion of the negative electrode terminal 9made of copper or a copper alloy. The sealing plate 2 has a thirdprotrusion 2 f and a fourth protrusion 2 g on the battery outer surface.The sealing plate 2 has a third recess 2 h around the third protrusion 2f and has a fourth recess 2 i around the fourth protrusion 2 g. Thesecond insulating member 81 is preferably fitted to the sealing plate 2.

In the prismatic secondary battery 20 according to the embodiment, thethermal resistance of the second insulating member 80 is higher than thethermal resistance of the first insulating member 10 made of resin onthe positive electrode terminal 7 side, while the thermal resistance ofthe second insulating member 81 is higher than the thermal resistance ofthe first insulating member 11 made of resin on the negative electrodeterminal 9 side. However, the thermal resistance of the secondinsulating member is not necessarily higher than the thermal resistanceof the first insulating member made of resin on both the positiveelectrode terminal 7 side and the negative electrode terminal 9 side. Inother words, the thermal resistance of the second insulating member ishigher than the thermal resistance of the first insulating member madeof resin on at least one of the positive electrode terminal 7 side andthe negative electrode terminal 9 side.

Battery Pack

A battery pack can be produced by connecting the prismatic secondarybatteries 20 according to the embodiment in parallel. FIG. 5 is a topview of a battery pack 200 including two batteries in parallel×threeunits in series, where three units of two prismatic secondary batteries20 connected in parallel are connected in series. A busbar 90 made ofmetal is fastened with the bolt 86 and a nut 87 attached to the externalconductive member 85 or the external conductive member 88 of eachprismatic secondary battery 20. The adjacent prismatic secondarybatteries 20 are electrically connected to each other with the busbar90. The busbar 90 is preferably made of aluminum or an aluminum alloy.As not illustrated in the figure, the battery pack 200 may have endplates at the opposed ends, and the end plates can be connected to eachother with binding bars. Moreover, an insulating spacer, such as aninsulating sheet, can be disposed between the adjacent prismaticsecondary batteries 20. The number of the prismatic secondary batteries20 connected in parallel can also be changed appropriately. The numberof series-connected units of the prismatic secondary batteries 20connected in parallel can also be changed appropriately. The batterypack may be composed only of the prismatic secondary batteries 20connected in parallel.

A battery pack known in the related art may undergo the followingphenomena if an internal short circuit occurs in one of the prismaticsecondary batteries 20 connected in parallel.

The internal pressure of the battery case 100 of the prismatic secondarybattery 20 in which an internal short circuit has occurred increases asthe temperatures increases rapidly. Since the prismatic secondarybatteries 20 are connected in parallel, a current flows into theprismatic secondary battery 20 in which the internal short circuit hasoccurred from other prismatic secondary batteries 20. Thus, theprismatic secondary batteries 20 in the case where an internal shortcircuit occurs in the prismatic secondary batteries 20 connected inparallel tends to reach a high temperature more rapidly and tends toreach a higher temperature than those in the case where an internalshort circuit occurs in the prismatic secondary batteries 20 that arenot connected in parallel.

In the prismatic secondary battery 20 in which the internal shortcircuit has occurred, the current interrupting mechanism 30 operates inresponse to an increase in the internal pressure of the battery case100. The operation of the current interrupting mechanism 30 causesdisconnection of the conduction path between the positive electrodeplate and the positive electrode terminal 7 and thus terminates thecurrent flow from other prismatic secondary batteries 20 into theprismatic secondary battery 20 in which the internal short circuit hasoccurred.

However, there is a case where the prismatic secondary battery 20 inwhich an internal short circuit has occurred reaches a very hightemperature. In this case, the high temperature may lead to melting ofthe first insulating member 10 made of resin, which insulates betweenthe positive electrode terminal 7 and the sealing plate 2, and the firstinsulating member 11 made of resin, which insulates between the negativeelectrode terminal 9 and the sealing plate 2. If the first insulatingmember 10 and the first insulating member 11 melt, the positiveelectrode terminal 7 and the negative electrode terminal 9 both comeinto contact with the sealing plate 2. This forms a conduction path ofpositive electrode terminal 7-sealing plate 2-negative electrodeterminal 9 and thus forms a closed circuit in the prismatic secondarybatteries 20 connected in parallel. As a result, a large current mayflow again into the prismatic secondary batteries 20 connected inparallel, and an abnormal event may occur in prismatic secondarybatteries 20 different from the prismatic secondary battery 20 in whicha short circuit has occurred.

In the prismatic secondary battery 20 according to the embodiment, thesecond insulating member 80 having higher thermal resistance than thefirst insulating member 10 is disposed between the sealing plate 2 andthe external conductive member 85 connected to the positive electrodeterminal 7. Therefore, even if the prismatic secondary battery 20becomes a high-temperature state so that the first insulating member 10melts, the second insulating member 80 keeps the external conductivemember 85 and the sealing plate 2 distant from each other. The positiveelectrode terminal 7 connected to the external conductive member 85 isthus unlikely to move toward the sealing plate 2. This can avoidelectrical connection between the positive electrode terminal 7 and thesealing plate 2. Therefore, even if an internal short circuit occurs inthe prismatic secondary batteries 20 connected in parallel as describedabove, a conduction path is formed separately after operation of thecurrent interrupting mechanism 30. This can avoid the flow of a largecurrent into other prismatic secondary batteries 20.

In the case where the first insulating member 10 disposed between thepositive electrode terminal 7 and the sealing plate 2 and the secondinsulating member 80 disposed between the external conductive member 85and the sealing plate 2 are separate members, the above-described issuecan be solved with a simple method while the airtightness of theprismatic secondary battery 20 can be effectively avoided fromdecreasing.

The second insulating member is preferably a member having higherthermal resistance than the first insulating member.

For example, the second insulating member may have a higher meltingpoint than the first insulating member. The second insulating member ispreferably a liquid crystal polymer. The liquid crystal polymer may havea structure based on p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid,or the like. The liquid crystal polymer may contain a ceramic fiber orceramic particles. Examples of suitable ceramics include alumina,zirconia, titania, silica, and glass.

Alternatively, the second insulating member may be a ceramic member madeof, for example, alumina, zirconia, titania, silica, or glass.

Alternatively, the second insulating member may be a resin membercontaining a ceramic filler, such as glass fiber. The resin may be, forexample, a thermosetting resin, such as a polyphenylene sulfide (PPS)resin or a phenolic resin.

The first insulating member is preferably made of, for example,polypropylene (PP), polyethylene (PE), polyphenylene sulfide (PPS),tetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinylether copolymer (PFA), or tetrafluoroethylene-ethylene copolymer (ETFE).This material can ensure sealing between the sealing plate and theterminal.

The prismatic secondary battery 20 according to the embodiment is anexample in which the pressure-sensitive current interrupting mechanism30 is provided between the positive electrode plate and the positiveelectrode terminal 7. However, the pressure-sensitive currentinterrupting mechanism 30 is not an essential element. Thepressure-sensitive current interrupting mechanism 30 may be replaced bya fuse part.

This embodiment illustrates an example in which the bolt is attached tothe external conductive member. The busbar may be weld-connected to theexternal conductive member, without attaching the bolt to the externalconductive member. Alternatively, the busbar may be used as an externalconductive member, and the busbar may be directly welded to theterminal.

The prismatic secondary battery 20 according to the embodiment is anexample in which the terminal is inserted from the battery outer side ofthe sealing plate and crimped on the battery inner side. The terminalmay be inserted from the battery inner side of the sealing plate andcrimped onto the external conductive member on the battery outer side.

Modification 1

As illustrated in FIG. 6, in a prismatic secondary battery according toModification 1, no bolt is attached to an external conductive member 185connected to a positive electrode terminal 7. A busbar 190 is directlyweld-connected to the external conductive member 185. Preferably, abusbar 190 is also directly weld-connected to an external conductivemember connected to a negative electrode terminal 9.

Modification 2

As illustrated in FIG. 7, in a prismatic secondary battery according toModification 2, a busbar 290 is directly connected to a positiveelectrode terminal 7. The busbar 290 is directly welded to the positiveelectrode terminal 7. This configuration provides a lightweight batterypack with low resistance.

A part of the positive electrode terminal 7 is inserted into thethrough-hole of the busbar 290. The busbar 290 is disposed on a flangepart 7 a of the positive electrode terminal 7.

A second insulating member 280 is disposed between the busbar 290 andthe sealing plate 2. The thermal resistance of the second insulatingmember 280 is higher than the thermal resistance of the first insulatingmember 10. The second insulating member 280 is preferably fitted to thesealing plate 2.

Modification 3

A prismatic secondary battery according to Modification 3 has no currentinterrupting mechanism but has a positive electrode current collector106 including a fuse part 106 x.

As illustrated in FIG. 8, a first insulating member 10 is disposed onthe battery outer side around a positive electrode terminal attachmenthole 2 a of a sealing plate 2. An internal insulating member 111 and abase part 106 a of a positive electrode current collector 106 aredisposed on the battery inner side around the positive electrodeterminal attachment hole 2 a of the sealing plate 2. The firstinsulating member 10 and the internal insulating member 111 are eachmade of resin. The positive electrode terminal 107 has a flange part 107a and an insertion part 107 b. The flange part 107 a is located on thebattery outer side with respect to the sealing plate 2. The insertionpart 107 b extends from the flange part 107 a to the battery inner side.The insertion part 107 b is inserted from the battery outer side intothe through-hole of the first insulating member 10, the positiveelectrode terminal attachment hole 2 a, the through-hole of the internalinsulating member 111, and the through-hole of the base part 106 a ofthe positive electrode current collector 106. The edge of the insertionpart 107 b is then crimped. As a result, a crimped part 107 c is formedin the insertion part 107 b. The crimped part 107 c is preferably weldedto a base part 106 a.

The positive electrode current collector 106 has a lead part 106 b,which extends from the base part 106 a toward the electrode body 3 andis connected to a positive electrode core-exposed portion 4. Thepositive electrode current collector 106 has the fuse part 106 x. Thefuse part 106 x can be formed by providing the positive electrodecurrent collector 106 with, for example, an opening, a cutout, or a thinportion, that is, a part having a smaller cross-sectional area thanother parts.

If an internal short circuit occurs in one prismatic secondary batteryin a battery pack including prismatic secondary batteries connected inparallel, a current flows into the prismatic secondary battery in whichthe internal short circuit has occurred from other prismatic secondarybatteries, and the fuse part 106 x melts and breaks. However, there is apossibility that the prismatic secondary battery in which the internalshort circuit has occurred becomes a high-temperature state, and thefirst insulating member 10 on the positive electrode side and a firstinsulating member 11 on the negative electrode side melt to form aconduction path of positive electrode terminal-sealing plate-negativeelectrode terminal.

In a prismatic secondary battery according to Modification 3, a secondinsulating member 280 having higher thermal resistance than a firstinsulating member 10 is disposed between the sealing plate 2 and abusbar 290 connected to the positive electrode terminal 107. Even if theprismatic secondary battery becomes a high-temperature state, the secondinsulating member thus keeps the distance between the busbar 290 and thesealing plate 2. Therefore, even if the first insulating member 10melts, the positive electrode terminal 107 connected to the busbar 290is unlikely to move toward the sealing plate 2. This can avoidelectrical connection between the positive electrode terminal 107 andthe sealing plate 2.

Modification 4

FIG. 9 is a view corresponding to FIG. 4 for a prismatic secondarybattery according to Modification 4.

The positive electrode current collector 206 includes a base part 206 aand an insertion part 206 b. The base part 206 a is located between thesealing plate 2 and an electrode body 3. The insertion part 206 bextends from the base part 206 a to the battery outer side. The positiveelectrode current collector 206 has a lead part 206 d, which extendsfrom the base part 206 a toward the electrode body 3 and is connected toa positive electrode core-exposed portion 4. The base part 206 a has afuse part 206 x. The insertion part 206 b of the positive electrodecurrent collector 206 functions as a positive electrode terminal. Afirst insulating member 110 made of resin is disposed between theinsertion part 206 b and the sealing plate 2. The interface between thesealing plate 2 and the insertion part 206 b is sealed with the firstinsulating member 110. A second insulating member 380 is disposed on thebattery outer surface of the sealing plate 2. An external conductivemember 385 is disposed on the second insulating member 380. Theinsertion part 206 b of the positive electrode current collector 206 isinserted into the through-hole of the external conductive member 385 andcrimped onto the external conductive member 385. As a result, a crimpedpart 206 c is formed. A busbar 390 is weld-connected to the externalconductive member 385.

In a battery pack including the prismatic secondary batteries accordingto Modification 4 connected in parallel, the second insulating member380 keeps the distance between the external conductive member 385 andthe sealing plate 2 even if the prismatic secondary battery becomes ahigh-temperature state so that the first insulating member 110 melts.Thus, the insertion part 206 b, which serves as a positive electrodeterminal connected to the external conductive member 385, is unlikely tomove toward the sealing plate 2. This can avoid electrical connectionbetween the sealing plate 2 and the insertion part 206 b, which servesas a positive electrode terminal.

Modification 5

A prismatic secondary battery according to Modification 5 differs fromthe prismatic secondary battery according to Modification 4 in theconfigurations of a first insulating member, a second insulating member,and a busbar.

As illustrated in FIG. 10, the prismatic secondary battery according toModification 5 includes a second insulating member 480 between a busbar490 and a sealing plate 2. The second insulating member 480 is fitted tothe sealing plate 2. A first insulating member 10 is disposed betweenthe sealing plate 2 and an insertion part 206 b, which serves as apositive electrode terminal. The thermal resistance of the secondinsulating member 480 is higher than the thermal resistance of a firstinsulating member 10.

In a battery pack including the prismatic secondary batteries accordingto Modification 5 connected in parallel, the second insulating member480 keeps the distance between the busbar 490 and the sealing plate 2even if the prismatic secondary battery becomes a high-temperature stateso that the first insulating member 10 melts. Thus, the insertion part206 b, which serves as a positive electrode terminal connected to thebusbar 490 through the external conductive member 385, is unlikely tomove toward the sealing plate 2. This can avoid electrical connectionbetween the sealing plate 2 and the insertion part 206 b, which servesas a positive electrode terminal.

Others

Modifications 1 to 5 illustrate examples in which the thermal resistanceof the second insulating member is higher than the thermal resistance ofthe first insulating member on the positive electrode terminal side.However, the thermal resistance of the second insulating member may behigher than the thermal resistance of the first insulating member on thenegative electrode terminal side. The thermal resistance of the secondinsulating member is higher than the thermal resistance of the firstinsulating member on at least one of the positive electrode terminalside and the negative electrode terminal side.

The embodiment and Modifications 1 to 5 illustrate examples in which thepositive electrode terminal and the negative electrode terminal areelectrically insulated from the sealing plate. However, at least one ofthe positive electrode terminal and the negative electrode terminal maybe electrically connected to the sealing plate.

The components that are not described in Modifications 1 to 5 may be thesame as those in the prismatic secondary battery 20 according to theembodiment.

The structure of the electrode body is not limited. The electrode bodymay be an electrode body including a strip-shaped positive electrodeplate and a strip-shaped negative electrode plate that are wound with astrip-shaped separator interposed therebetween. The electrode body maybe a stacked electrode body including positive electrode plates andnegative electrode plates that are stacked with separators eachinterposed therebetween. A plurality of electrode bodies may be placedin the battery case.

The secondary battery according to the present invention can be used ina battery pack including secondary batteries all connected in series.However, the secondary battery according to the present invention isvery effective when used in a battery pack in which at least twosecondary batteries are connected in parallel.

The secondary battery is preferably a non-aqueous electrolyte secondarybattery and more preferably a lithium-ion secondary battery. Thepositive electrode plate, the negative electrode plate, the separator,the electrolyte, and the like may be composed of known materials.

The melting point of the second insulating member is preferably 250° C.or more, more preferably 280° C. or more, and still more preferably 300°C. or more.

The deflection temperature under load of the second insulating member ispreferably higher than the deflection temperature under load of thefirst insulating member. The deflection temperature under load of thesecond insulating member is preferably 250° C. or more, more preferably280° C. or more, and still more preferably 300° C. or more.

The second insulating member may be a high melting point resin, such asliquid crystal polymer (LCP), polyether ether ketone (PEEK),polyphenylene sulfide (PPS), polyimide (PI), polyetherimide (PEI), orpolyether sulfone (PES). Such a resin may contain a ceramic fiber orceramic particles. Alternatively, a ceramic member may be disposed insuch a resin.

The third insulating member disposed between the sealing plate and theconductive member included in the current interrupting mechanism may beintegrated with the first insulating member to form one component. Theinternal insulating member disposed between the sealing plate and thecurrent collector may be integrated with the first insulating member toform one component.

The thermal resistance of the third insulating member disposed betweenthe sealing plate and the conductive member included in the currentinterrupting mechanism may be higher than the thermal resistance of thefirst insulating member. The thermal resistance of the internalinsulating member disposed between the sealing plate and the currentcollector may be higher than the thermal resistance of the firstinsulating member.

While detailed embodiments have been used to illustrate the presentinvention, to those skilled in the art, however, it will be apparentfrom the foregoing disclosure that various changes and modifications canbe made therein without departing from the spirit and scope of theinvention. Furthermore, the foregoing description of the embodimentsaccording to the present invention is provided for illustration only,and is not intended to limit the invention.

What is claimed is:
 1. A secondary battery comprising: an electrode bodythat includes a positive electrode plate and a negative electrode plate;an outer body that has an opening and houses the electrode body; asealing plate that is made of metal and seals the opening; and aterminal that is electrically connected to the positive electrode plateor the negative electrode plate, wherein the sealing plate has aterminal attachment hole, the terminal penetrates the terminalattachment hole, an external conductive member is connected to a portionof the terminal located on a battery outer side with respect to thesealing plate, a conduction path between the positive electrode plate orthe negative electrode plate and the terminal is provided with at leastone of a current interrupting mechanism and a fuse part, a firstinsulating member made of resin is disposed between the sealing plateand the terminal, a second insulating member having higher thermalresistance than the first insulating member is disposed between theexternal conductive member and the sealing plate, and the secondinsulating member is fitted to the sealing plate.
 2. The secondarybattery according to claim 1, wherein the current interrupting mechanismis disposed, and the current interrupting mechanism is apressure-sensitive current interrupting mechanism that operates when aninternal pressure of a battery case including the outer body and thesealing plate reaches a predetermined value or higher.
 3. The secondarybattery according to claim 1, wherein the second insulating member is aresin member having a higher melting point than a resin that constitutesthe first insulating member.
 4. The secondary battery according to claim1, wherein the second insulating member is made of a liquid crystalpolymer.
 5. The secondary battery according to claim 1, wherein thesecond insulating member is a resin member containing a ceramic filler.6. The secondary battery according to claim 1, wherein the secondinsulating member is a ceramic member.
 7. The secondary batteryaccording to claim 1, further comprising a bolt connected to theexternal conductive member.
 8. The secondary battery according to claim1, wherein the external conductive member is a busbar.
 9. A battery packcomprising a plurality of the secondary batteries according to claim 1,wherein the plurality of secondary batteries includes at least twosecondary batteries connected in parallel.